Process for the electrodeposition of metals.



UNITED STATES PATENT oEEIoE.

'JosEF AUGUST NUSSBAUM, OF CHARLOTTENBURG, GERMANY, AS-

-SIGNOR TO. SIEMENS & HALSKE AKTIENGESELLSCHAFT, OF

BERLIN, GERMANY.

PROCESS FOR THE ELECTRODEPOSITION OF METALS.

Specification of Letters Patent.

Patented Sept. 25, 1906.

Application filed November 28, 1905. Serial No. 289.483.

To all whom it r na/y concern.-

Beit known that I, JosEF AUGUST Nuss- BAUM, a subject of the Austrian Em eror, re-

' objectionable crystal formations in the de-.

posited metal and to produce metal deposits in thick dense coherent layers. 1

A further object of my invention is to obtain such deposits from any of the salts of the metal to be deposited without being compelled to use the few costly and poisonous salts to which electrolytic processes for the separation of the metals have heretofore been restricted.

It has been known for some time .that the deposition of metals by the aid of the electric current for certain technical purposes is impracticable, for the reason that many metals have the tendency to deposit in the form of pointed or' bud-like crystals, so that in such cases it hasbeen impossible to obtain dense uniform metal surfaces. Up to the present the materials employed for obtaining the dense coherent metal deposits absolutely necessary for certain technical purposessuch as galvano-plastic, electrotyping, and refining of metals, and-similar rocesses-have consisted of materials which are prone to the objectionable crystal formation above referred to-as, for instance, with gold, silver, tin,

cadmium, &c., the metal has been deposited from electrolytes which contain the metal, in

the form of a complex saltfor example, with gold, silver, and copper from potassium cyanid solutions, with cadmium and tin from oxalic-acid solutions, &c. My invention contemplates the substitution for the expensive and particular processes above-indicated,

which are available in the nature of the case only to limited applications, of a cheaper simpler process of more general application. The formation of such dendritic aggregates in the electrodeposition of metals appears most likely to be due to the fact that t e place of setting free ofthe metal ions is' different from the place ofthe separation as metal, so that after the setting free of the metal ions the metallic separation does not at once follow, but an unstable intermediate form still remains fora short time in solution, from which metal deposits first here and there. where the conditions favorable to its separation exist such, for instance, at those places where crystals already exist, which crystals will therefore grow larger at the ex ense of adjacent portions of the cathode, ta g on a form of needles, foliations, &c. It is not important whether this unstable form be a very unstable lower oxidation stage of the metal in question (in this connection the partial setting free of cuprous salt from cupric salt is very well known, which on account of its instability spontaneously decomposes into cupric salt and copper, whereby the copper has time to form crystals, so that it appears as if the current deposits crystalline copper direct) or whether, as a second possible species of the unstable form, the metal passing over a colloidal dissolved condition comes down. In further sup ort of the intermediate formation of the fewer oxidation stage the circumstance, among others, that those metals which are particularly prone to such objectionable crystal formations in their electrodeposition are, in fact, known in a very unstable lower oxidation stage, which under suitable conditions easily decomposes into a higher sta e, and the metal Cd O Ag O, Cu O, Au &c., the salts of which for the most part are not known in solid form, because they are easily decomposed.

In view of the above considerations it will be apparent that if conditions be established in the electrolyte which hinder or prevent the.

changing of place of the unstable intermedi- I with technical advantage, I have discovered that the addition to the electrolyte of a certain group of slimy or colloidal substances are well suited. The colloids behave in electrolysis in various manners, as appears from the work of Bredig, Hardy, and other investigators, (see, for example, Bredigs report upon the colloidal condition, Zeitschriftfttr Elcktrochemic, IX, 1903, page 739,) in so far as with some of them a wandering to the anode takes place and with others a similar wanderingto the cathode occurs, which is to be traced to a cataphoretic effect.

For the purpose above designated only those colloids which wander to the cathode are suitable, and their favorable influences in preventing dendritic crystal formation are readily explained by their action in forming anintermediary colloidal layer -at those places on the cathode where crystal points tend to grow by the above-explained local shifting of themetal separation, which causes at these places a strong current density, as a result of which an increased .traveling of the colloids to those places takes place. The colloidal layer acts as a diaphragm, since it checks diffusion and circulation. In the progress of the electrolysis these deposition centers shift from place to place, so that the process may be explained as a fluctuating diaphragm on the cathode. In consequence of this with many colloids it suffices, as extended experiments have shown, to make a relatively small addition to produce a perfectly smooth deposit even with those metals which are particularly prone to dendritic crystal formation. As instances of colloids which I have found particularly effective in many different proportions on account of their cathode wandering may be named, among others, the seed mucilages, (linseed, for example,) roots or bulbs mucilage, (salep,) vegetable gums, glutinous plant saps, albumen, and their hydrolization and transformation products of animal and vegetable origin, (glutin, condrin, mucin, &c.) Also inorganic colloids may in some circumstances be used with advantage.

One of the important features of advantage of the above invention lies in the fact that electrolytic deposition of practical metal deposits is now no longer restricted, as formerly, to a few costly and for the most part poisonous metal salts, but with minute additions of any of the above-named substances the metals may be deposited with certainty and in compact form from any of their salts. These additions may be in such quantities as do not materially increase the viscosity of the electrolyte.

As an example illustrative of my invention I ma cite as an instance the electrolytic refining of copper. Up to the present this has been accomplished by means of a solution of copper sulfate or of some other cupric salt, notwithstanding that with the same current cuprous salts give double the yield of copfper, since the electrochemical equivalent 0 the copper therein is twice as j great. The reason why the cuprous salts 1 for example, copper chlorid.-have not been "this case it is suiiicient to add to the solution about .2 per cent. of a colloid which has the property of wandering to the cathodefor example, flaxor linseed mucilage or salep mucilage. The current density may be the same as in the present known process of copper refining, and also the content of the solution in copper may be the same as ordinarily employed.

Having thus described my invention, what I claim, and desire to secureby Letters Patent, is- V r 1. The process of electrodepositing metals to form a compact coherent layer which consists in adding to the electrolyte a colloidal substance which has the property of wandering to the cathode and subjecting the electro lyte to electrolysis.

2. The process of electrodepositing metals to obtain a compact coherent deposit or layer which consists in forming at the cathode in the process of the electrolysis a colloidal layer which ,acts as a diaphragm, substantially as and for the purpose described.

3. The process of electrodepositing metals which consists in adding to the electrolyte in minute quantity a colloidal substance which has the characteristic of wandering to, the cathode, and subjecting the electrolyte to electrolysis.

4. The process of electrodepositing metals from solutions having a tendency to deposit in crystals, said process consisting in a ding a colloidal substance having the property of traveling to the cathode, to said solution prior to electrolysis and subjecting said solution so treated to electrolysis.

5. The process of obtaining electrolytic metal deposits of a uniform compact coherent form, which consists in electrolytically interposing a fluctuating colloidal layer which acts as a diaphragm at the surface of the cathode, substantially as described.

6. The process of obtaining electrodeposits of a uniform, compact and coherent character, said process consisting in forming, in the process of electrolysis, a colloidal layer which acts as a diaphragm at those places on the cathode where the current density tends to increase beyond that at other places on the cathode.

JOSEF AUGUST NUSSBAUM. 

